Pulmonary dysfunction is the most frequent life-threatening complication of AIDS. The etiology and response to therapy has been assessed by serial bronchoscopies with biopsy in AIDS patients. A) Pneumocystis. Pneumonia has been the most frequent etiology. Histopathology of initial biopsies has been shown to be similar to non-AIDS patients, but on the followup biopsy after three weeks of therapy, AIDS patients still have abundant organisms, which has not been the case with non-AIDS patients. The significance of this finding is being assessed by long-term follow-up and statistical analysis. B) Kaposi's sacroma. In patients with known KS of the skin or lymph nodes, KS is the sole cause of pulmonary dysfunction in 20% of cases. Diagnosis can only by unequivocally established by open lung biopsy. Radiation and chemotherapy have some role in pallitating these patients. These are being assessed. C) Cytomegalovirus. Two patients with CMV pneumonia have been cured with a new investigational drug, DHPG. Additional patients are being sought. D) Nonspecific pneumonitis. In 20-40% of cases, the etiology of penumonitis cannot be recognized. The role of HIB in causing this pneumonitis is being assessed. The significance of this project lies in determining methods to improve the quality and duration of survival in AIDS patients. This investigation has resulted in recognition that many patients have inflammation without discernible cause, an observation that will spare many patients being sent for follow-up open lung biopsies.